如何创建用户定义的JLabel，JTextField？

Question

Based on the title, how do I create a dynamic size of JLabel and JTextfield determined by user ?

I have a Main.java which takes user input and I'm creating a JFrame on another file ( Design3.java ) but the problem I encounter is how do I pass the value from the Main.java to Design3.java

Here is my code for the Design3.java file. Basically I'm stucked because the value I passed from Main.java the scope of the variable last for the Design3 method. How do I make it global because I need to create JLabel globally.

int numberOfSellers;

Label[] l = new Label[numberOfSellers];

public class Design3 {

    int numberOfSellers;

    Design3 nOS = new Design3();

    public Design3( int number_of_sellers )
    {
        nOS.setNumberOfSellers(number_of_sellers);

        JFrame newWindow = new JFrame("Test");

        newWindow.setVisible(true);
        newWindow.setSize(500,500);
        newWindow.setLayout(null);
    }

    public void setNumberOfSellers(int num)
    {
        this.numberOfSellers = num;
    }

}

Answer 1

Based on the title, how do I create a dynamic size of JLabel and JTextfield determined by user ?

What are you trying to do ? You can look into creating a custom class that extends JLabel and another custom class which extends JTextField .

Second, why does Design3 have an instance of Design3 ? I am sensing a lot of bad design here.

Third, look into the Swing MVC architecture.

Answer 2

Your question in a nutshell is: How can I have an object of one class change the state of an object in another class. Usually that translates into having one object change the state of the field(s) of another object.

Comments:

• There is no one-size fits all answer for this as it is a very broad and overly general question. That is why we are asking for clarification of your problem since the more specific your question, usually the more clear the answer.
• General ways to change the state of an object's field including via a constructor parameter. So you can give your GUI an int field say numberOfFoo and then give it a constructor parameter to match, and then when one class creates an instance of the other, it can pass the proper number into the first class's constructor.
• Or you could use a setter method such as setFoo(int foo) where one class can pass the number into the other class.

If you have a more specific question, then you'll have to delineate it further. For instance, if you want one object to monitor another object's field and respond to changes, then again as per my comment, you'll want to use some type of observer design pattern mechanism.